Light-emitting element, display module, lighting module, light-emitting device, display device, electronic device, and lighting device

ABSTRACT

A light-emitting element with improved heat resistance is provided without losing its advantages such as thinness, lightness, and low power consumption. A light-emitting element is provided which includes a first electrode, a second electrode, and an EL layer between the first electrode and the second electrode, in which the EL layer includes a layer containing a condensed aromatic compound or a condensed heteroaromatic compound, and a layer containing 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBPhen) in contact with the layer containing the condensed aromatic compound or the condensed heteroaromatic compound.

This application is a continuation of copending U.S. application Ser.No. 14/453,889, filed on Aug. 7, 2014 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, and a composition of matter. One embodiment of thepresent invention particularly relates to a semiconductor device, adisplay device, a light-emitting device, a driving method thereof, and amanufacturing method thereof. One embodiment of the present inventionparticularly relates to a light-emitting element, a display module, alighting module, a display device, a light-emitting device, anelectronic device, and a lighting device in which an organic compound isused as a light-emitting substance.

2. Description of the Related Art

In recent years, research and development of a light-emitting element(organic EL element) which uses an organic compound and utilizeselectroluminescence (EL) have been actively promoted. In the basicstructure of such a light-emitting element, an organic compound layercontaining a light-emitting substance (an EL layer) is provided betweena pair of electrodes. By voltage application to this element, lightemission from the light-emitting substance can be obtained.

Since such a light-emitting element is of self-light-emitting type, itis considered that the light-emitting element has advantages over aliquid crystal display, such as high visibility of pixels and no need ofbacklight, and is therefore suitable as a flat panel display element. Adisplay including such a light-emitting element is also highlyadvantageous in that it can be thin and lightweight. Besides, very highspeed response is one of the features of such an element.

Furthermore, an organic EL element can provide planar light emission.Thus, a large-area element can be easily formed. This feature isdifficult to obtain with point light sources typified by incandescentlamps and LEDs or linear light sources typified by fluorescent lamps.Thus, the light-emitting element also has great potential as a planarlight source which can be applied to a lighting device and the like.

A display or a lighting device including an organic EL element havingsuch features is applied to a variety of electronic devices and used ina variety of environments. For example, a display of an in-vehiclenavigation system or the like is constantly located in a car; adashboard of a sun-heated car in summer often reaches a temperature ashigh as or higher than 80° C. Since the above-described light-emittingelement is formed by stacking layers of a variety of organic compounds,it may deteriorate and become inoperative when placed in a hightemperature environment.

There is a demand for a highly heat resistant light-emitting elementwith reduced deterioration of characteristics even after it is placed ina high temperature environment as described above (see Patent Documents1, for example).

PATENT DOCUMENT

[Patent Document 1] Japanese Published Patent Application No. H10-340781

SUMMARY OF THE INVENTION

Therefore, it is an object of an embodiment of the present invention toprovide a light-emitting element with improved heat resistance.

It is an object of another embodiment of the present invention toprovide a light-emitting element with improved heat resistance withoutlosing its advantages such as thinness, lightness, and low powerconsumption. It is an object of another embodiment of the presentinvention to provide a novel light-emitting element.

It is an object of another embodiment of the present invention toprovide a display module, a lighting module, a light-emitting device, adisplay device, an electronic device, and a lighting device withexcellent heat resistance by using the above light-emitting element.

It is an object of another embodiment of the present invention toprovide a display module, a lighting module, a light-emitting device, adisplay device, an electronic device, and a lighting device withexcellent heat resistance by using the above light-emitting elementwithout losing its advantages such as thinness, lightness, and low powerconsumption.

It is only necessary that at least one of the above-described objects beachieved in the present invention.

One embodiment of the present invention is a light-emitting elementwhich includes a first electrode, a second electrode, and an EL layerbetween the first electrode and the second electrode. The EL layerincludes a layer containing a condensed aromatic compound or a condensedheteroaromatic compound, and a layer containing2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBPhen) in contact with the layer containing the condensed aromaticcompound or the condensed heteroaromatic compound.

One embodiment of the present invention is a light-emitting elementwhich includes a first electrode, a second electrode, and an EL layerbetween the first electrode and the second electrode. The EL layerincludes a layer containing a condensed aromatic compound or a condensedheteroaromatic compound having a condensed ring skeleton including threeor more rings, and a layer containing NBPhen in contact with the layercontaining the condensed aromatic compound or the condensedheteroaromatic compound.

Another embodiment of the present invention is a light-emitting elementhaving the above structure, in which the layer containing the condensedaromatic compound or the condensed heteroaromatic compound contains thecondensed heteroaromatic compound.

Another embodiment of the present invention is a light-emitting elementhaving the above structure, in which the condensed heteroaromaticcompound includes two nitrogen atoms in one condensed ring skeleton.

Another embodiment of the present invention is a light-emitting elementhaving the above structure and emitting phosphorescent light.

Another embodiment of the present invention is a light-emitting elementhaving the above structure, in which the layer containing the condensedheteroaromatic compound further contains iridium.

Another embodiment of the present invention is a light-emitting elementhaving the above structure, in which iridium is contained in a portionof the layer containing the condensed heteroaromatic compound and is notcontained in a region in contact with the layer containing NBPhen.

An embodiment of the present invention is a display module including anyof the above light-emitting elements.

An embodiment of the present invention is a lighting module includingany of the above light-emitting elements.

An embodiment of the present invention is a light-emitting deviceincluding any of the above light-emitting elements and a unit forcontrolling the light-emitting element.

An embodiment of the present invention is a display device including anyof the above light-emitting elements in a display portion and a unit forcontrolling the light-emitting element.

An embodiment of the present invention is a lighting device includingany of the above light-emitting elements in a lighting portion and aunit for controlling the light-emitting element.

An embodiment of the present invention is an electronic device includingany of the above light-emitting elements.

Note that the light-emitting device in this specification includes, inits category, an image display device with a light-emitting element. Inaddition, the light-emitting device includes all the following modules:a module in which a connector, such as an anisotropic conductive film ora tape carrier package (TCP), is attached to a light-emitting device; amodule in which a printed wiring board is provided at the end of a TCP;and a module in which an integrated circuit (IC) is directly mounted ona light-emitting device by a chip-on-glass (COG) method. Furthermore,light-emitting devices that are used in lighting equipment and the likeshall also be included.

One embodiment of the present invention can provide a light-emittingelement with improved heat resistance.

Another embodiment of the present invention can provide a light-emittingelement with improved heat resistance without losing its advantages suchas thinness, lightness, and low power consumption.

Another embodiment of the present invention can provide a displaymodule, a lighting module, a light-emitting device, a display device, anelectronic device, and a lighting device with excellent heat resistanceby using the above-described light-emitting element.

Another embodiment of the present invention can provide a displaymodule, a lighting module, a light-emitting device, a display device, anelectronic device, and a lighting device with excellent heat resistanceby using the above-described light-emitting element without losing itsadvantages such as thinness, lightness, and low power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic diagrams of light-emitting elements.

FIGS. 2A and 2B are schematic diagrams of an active matrixlight-emitting device.

FIGS. 3A and 3B are schematic diagrams of active matrix light-emittingdevices.

FIG. 4 is a schematic diagram of an active matrix light-emitting device.

FIGS. 5A and 5B are schematic diagrams of a passive matrixlight-emitting device.

FIGS. 6A and 6B illustrate a lighting device.

FIGS. 7A, 7B1, 7B2, 7C, and 7D illustrate electronic devices.

FIG. 8 illustrates a light source device.

FIG. 9 illustrates a lighting device.

FIG. 10 illustrates a lighting device.

FIG. 11 illustrates in-vehicle display devices and lighting devices.

FIGS. 12A to 12C illustrate an electronic device.

FIG. 13 shows current density-luminance characteristics of alight-emitting element 1 and a comparative light-emitting element 1.

FIG. 14 shows luminance-current efficiency characteristics of thelight-emitting element 1 and the comparative light-emitting element 1.

FIG. 15 shows voltage-luminance characteristics of the light-emittingelement 1 and the comparative light-emitting element 1.

FIG. 16 shows emission spectra of the light-emitting element 1 and thecomparative light-emitting element 1.

FIG. 17 shows current density-luminance characteristics of alight-emitting element 2 and a comparative light-emitting element 2.

FIG. 18 shows luminance-current efficiency characteristics of thelight-emitting element 2 and the comparative light-emitting element 2.

FIG. 19 shows voltage-luminance characteristics of the light-emittingelement 2 and the comparative light-emitting element 2.

FIG. 20 shows emission spectra of the light-emitting element 2 and thecomparative light-emitting element 2.

FIG. 21 shows current density-luminance characteristics of alight-emitting element 3 and a comparative light-emitting element 3.

FIG. 22 shows luminance-current efficiency characteristics of thelight-emitting element 3 and the comparative light-emitting element 3.

FIG. 23 shows voltage-luminance characteristics of the light-emittingelement 3 and the comparative light-emitting element 3.

FIG. 24 shows emission spectra of the light-emitting element 3 and thecomparative light-emitting element 3.

FIGS. 25A and 25B show high-temperature exposition test results(luminance changes) of the light-emitting elements 1 to 3 and thecomparative light-emitting elements 1 to 3.

FIGS. 26A and 26B show high-temperature exposition test results (voltagechanges) of the light-emitting elements 1 to 3 and the comparativelight-emitting elements 1 to 3.

FIG. 27 shows current density-luminance characteristic of light-emittingelements 4 to 6.

FIG. 28 shows luminance-current efficiency characteristics of thelight-emitting elements 4 to 6.

FIG. 29 shows voltage-luminance characteristics of the light-emittingelements 4 to 6.

FIG. 30 shows emission spectra of the light-emitting elements 4 to 6.

FIG. 31 shows time dependence of normalized luminance of thelight-emitting elements 4 to 6.

FIG. 32 shows a UPLC chromatogram of a sample 1.

FIG. 33 shows a UPLC chromatogram of a sample 2.

FIG. 34 shows a UPLC chromatogram of a sample 3.

FIG. 35 shows a mass spectrum of an impurity 1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. Note that the present invention is notlimited to the following description, and it will be easily understoodby those skilled in the art that various changes and modifications canbe made without departing from the spirit and scope of the presentinvention. Therefore, the present invention should not be construed asbeing limited to the description in the following embodiments.

Embodiment 1

The heat resistance of a light-emitting element is known to greatlydepend on the heat resistance of a material used (e.g., Tg or thermaldecomposition temperature), but other factors have not been examined somuch. The present inventors found out that a stacked-layer structure ofa light-emitting element also affects heat resistance, and invented alight-emitting element with improved heat resistance compared with thoseof conventional ones, in which a layer containing NBPhen and a layercontaining a condensed aromatic compound or a condensed heteroaromaticcompound are stacked as an electron-transport layer.

FIG. 1A illustrates a schematic diagram of a light-emitting element ofone embodiment of the present invention. The light-emitting element hasat least a pair of electrodes (a first electrode 101 and a secondelectrode 102) and an EL layer 103 including a layer 114 n containing acondensed aromatic compound or a condensed heteroaromatic compound and alayer 114 m containing NBPhen in contact with the layer 114 n containingthe condensed aromatic compound or the condensed heteroaromaticcompound.

FIG. 1A also illustrates a hole-injection layer 111, a hole-transportlayer 112, a light-emitting layer 113, and an electron-injection layer115 in the EL layer 103. However, this stacked-layer structure is anexample, and the structure of the EL layer 103 in the light-emittingelement of one embodiment of the present invention is not limitedthereto. Note that in FIG. 1A, the first electrode 101 functions as ananode, and the second electrode 102 functions as a cathode.

In the light-emitting element of this embodiment, the layer 114 mcontaining NBPhen is in contact with the layer 114 n containing thecondensed aromatic compound or the condensed heteroaromatic compound.Since the layer 114 m containing NBPhen has an electron-transportproperty, it is preferably provided closer to the cathode than alight-emitting region is. The layer 114 m containing NBPhen may be incontact with the electron-injection layer 115 or the second electrode102 on the side opposite to the side in contact with the layer 114 ncontaining the condensed aromatic compound or the condensedheteroaromatic compound.

The condensed aromatic compound or the condensed heteroaromatic compoundis preferably a compound having a condensed ring skeleton includingthree or more rings. This is because the interface between NBPhen andthe compound having the condensed ring skeleton including three or morerings is thermally and electrically very stable.

The light-emitting element having this structure of one embodiment ofthe present invention shows a small decrease in luminance even when keptin an environment at high temperature (e.g., 85° C. or higher). In thecase where the layer 114 n containing the condensed aromatic compound orthe condensed heteroaromatic compound contains the condensedheteroaromatic compound, a change in drive voltage can also be reduced.

In the case where the layer 114 n containing the condensed aromaticcompound or the condensed heteroaromatic compound contains the condensedheteroaromatic compound, the condensed heteroaromatic compoundpreferably includes two nitrogen atoms in one condensed ring skeletonbecause this enables the light-emitting element to have high reliabilityand also contributes to a decrease in drive voltage.

The condensed heteroaromatic compound is suitable as a host material fora phosphorescent light-emitting substance or as a material of anelectron-transport layer adjacent to a phosphorescent light-emittinglayer; therefore, the light-emitting element is preferably alight-emitting element which emits phosphorescent light. Aphosphorescent light-emitting element having the above structure canhave high reliability with improved heat resistance, and can have bothhigh reliability and high emission efficiency due to the use ofphosphorescent light emission.

Examples of compounds which can be suitably used as the condensedaromatic compound or the condensed heteroaromatic compound include thefollowing. Suitable examples of the condensed aromatic compound includecompounds having condensed ring skeletons each including three or morerings, e.g., anthracene compounds such as9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(abbreviation: 2mBnfPPA), and9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene(abbreviation: FLPPA) and tetracene compounds such as5,12-bis(2,4-diphenylphenyl)tetracene. Among these compounds, anthracenecompounds are particularly preferable because a light-emitting elementwith long lifetime can be easily obtained. Examples of the condensedheteroaromatic compound include heterocyclic compounds having polyazoleskeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); condensed heterocyclic compounds includingthree or more rings having diazine skeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II), and2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq); and condensed heterocyclic compounds havingpyridine skeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviation:2mDBTPDBQu-II) and2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}dibenzo[f,h]quinoline(abbreviation: 2mDBTBPDBQu-II). Among the above compounds, heterocycliccompounds having diazine skeletons and heterocyclic compounds havingpyridine skeletons have high reliability and are thus preferable.Heterocyclic compounds having diazine (pyrimidine or pyrazine) skeletonshave a high electron-transport property and contribute to a decrease indrive voltage; thus, among the above compounds, dibenzoquinoxalinederivatives such as 2mDBTPDBq-II, 2mDBTBPDBq-II, and 2mCzBPDBq areparticularly suitable.

Embodiment 2

In this embodiment, a detailed example of the structure of thelight-emitting element described in Embodiment 1 will be described belowwith reference to FIG. 1A.

The light-emitting element in this embodiment includes, between the pairof electrodes, the EL layer including a plurality of layers. In thisembodiment, the light-emitting element includes the first electrode 101,the second electrode 102, and the EL layer 103 which is provided betweenthe first electrode 101 and the second electrode 102. Note that thefollowing description is made on the assumption that the first electrode101 functions as an anode and that the second electrode 102 functions asa cathode.

Since the first electrode 101 functions as the anode, the firstelectrode 101 is preferably formed using any of metals, alloys,electrically conductive compounds with a high work function(specifically, a work function of 4.0 eV or more), mixtures thereof, andthe like. Specifically, for example, indium oxide-tin oxide (ITO: indiumtin oxide), indium oxide-tin oxide containing silicon or silicon oxide,indium oxide-zinc oxide, indium oxide containing tungsten oxide and zincoxide (IWZO), and the like can be given. Films of these electricallyconductive metal oxides are usually formed by a sputtering method butmay be formed by application of a sol-gel method or the like. In anexample of the formation method, indium oxide-zinc oxide is deposited bya sputtering method using a target obtained by adding 1 wt % to 20 wt %of zinc oxide to indium oxide. Further, a film of indium oxidecontaining tungsten oxide and zinc oxide (IWZO) can be formed by asputtering method using a target in which tungsten oxide and zinc oxideare added to indium oxide at 0.5 wt % to 5 wt % and 0.1 wt % to 1 wt %,respectively. Besides, gold (Au), platinum (Pt), nickel (Ni), tungsten(W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper(Cu), palladium (Pd), nitrides of metal materials (e.g., titaniumnitride), and the like can be given. Graphene can also be used. Notethat when a composite material described later is used for a layer whichis in contact with the first electrode 101 in the EL layer 103, anelectrode material can be selected regardless of its work function.

There is no particular limitation on the stacked-layer structure of theEL layer 103 as long as the EL layer 103 has the structure described inEmbodiment 1. For example, the EL layer 103 can be formed by combining ahole-injection layer, a hole-transport layer, a light-emitting layer, anelectron-transport layer, an electron-injection layer, acarrier-blocking layer, an intermediate layer, and the like asappropriate. In this embodiment, the EL layer 103 has a structure inwhich the hole-injection layer 111, the hole-transport layer 112, thelight-emitting layer 113, an electron-transport layer 114, and theelectron-injection layer 115 are stacked in this order over the firstelectrode 101. Among these layers, the electron-transport layer 114 hasa structure in which the layer 114 n containing the condensed aromaticcompound or the condensed heteroaromatic compound and the layer 114 mcontaining NBPhen are stacked. Specific examples of materials used foreach layer are given below.

The hole-injection layer 111 contains a substance with a highhole-injection property. Molybdenum oxide, vanadium oxide, rutheniumoxide, tungsten oxide, manganese oxide, or the like can be used.Alternatively, the hole-injection layer 111 can be formed using aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) and copper phthalocyanine (CuPc), an aromatic amine compound suchas 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB) and N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD), or a high molecular compound such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS).

Alternatively, a composite material in which a substance having ahole-transport property contains a substance having an acceptor propertycan be used for the hole-injection layer 111. Note that the use of sucha substance having a hole-transport property which contains a substancehaving an acceptor property enables selection of a material used to forman electrode regardless of its work function. In other words, besides amaterial having a high work function, a material having a low workfunction can also be used for the first electrode 101. As the substancehaving an acceptor property,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Oxides of the metals that belong to Groups 4to 8 of the periodic table can be given. Specifically, vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferable inthat their electron-accepting property is high. Among these oxides,molybdenum oxide is particularly preferable in that it is stable in theair, has a low hygroscopic property, and is easy to handle.

As the substance having a hole-transport property which is used for thecomposite material, any of a variety of organic compounds such asaromatic amine compounds, carbazole derivatives, aromatic hydrocarbons,and high molecular compounds (e.g., oligomers, dendrimers, or polymers)can be used. Organic compounds that can be used as the substance havinga hole-transport property in the composite material are specificallygiven below.

Examples of the aromatic amine compounds areN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

Specific examples of carbazole derivatives that can be used for thecomposite material are3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Other examples of carbazole derivatives that can be used for thecomposite material are 4,4′-di(N-carbazolyl)biphenyl (abbreviation:CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of aromatic hydrocarbons that can be used for the compositematerial are 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation:t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Besides, pentacene, coronene, and the like can also be used.The aromatic hydrocarbon which has a hole mobility of 1×10⁻⁶ cm²/Vs ormore and which has 14 to 42 carbon atoms is particularly preferable.

Note that the aromatic hydrocarbons that can be used for the compositematerial may have a vinyl skeleton. Examples of the aromatic hydrocarbonhaving a vinyl group are 4,4′-bis(2,2-diphenylvinyl)biphenyl(abbreviation: DPVBi) and9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

A high molecular compound such as poly(N-vinylcarbazole) (abbreviation:PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD) can also be used.

By providing a hole-injection layer, a high hole-injection property canbe achieved to allow a light-emitting element to be driven at a lowvoltage.

The hole-transport layer 112 contains a substance having ahole-transport property. Examples of the substance having ahole-transport property are aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).The substances mentioned here have high hole-transport properties andare mainly ones that have a hole mobility of 10⁻⁶ cm²/Vs or more. Anorganic compound given as an example of the substance having ahole-transport property in the composite material described above canalso be used for the hole-transport layer 112. A high molecular compoundsuch as poly(N-vinylcarbazole) (abbreviation: PVK) andpoly(4-vinyltriphenylamine) (abbreviation: PVTPA) can also be used. Notethat the layer that contains a substance having a hole-transportproperty is not limited to a single layer, and may be a stack of two ormore layers including any of the above substances.

The light-emitting layer 113 may be a layer emitting fluorescent light,a layer emitting phosphorescent light, or a layer emitting thermallyactivated delayed fluorescent (TADF) light. Furthermore, thelight-emitting layer 113 may be a single layer or include a plurality oflayers containing different light-emitting substances.

Examples of a material which can be used as a fluorescent light-emittingsubstance in the light-emitting layer 113 are as follows. Other variousfluorescent light-emitting substances can also be used.

The examples include5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6FLPAPrn),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPm),N,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N″-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N″-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N″-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), 9-triphenylanthracen-9-amine (abbreviation:DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone (abbreviation: DPQd),rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene(abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM). Condensed aromatic diamine compounds typifiedby pyrenediamine compounds such as 1,6FLPAPrn and 1,6mMemFLPAPrn areparticularly preferable because of their high hole-trapping properties,high emission efficiency, and high reliability.

Preferable examples of host materials in which the fluorescentlight-emitting substance is dispersed are as follows.

The examples include anthracene compounds such as9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(abbreviation: 2mBnfPPA), and9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene(abbreviation: FLPPA). The use of a substance having an anthraceneskeleton as the host material makes it possible to obtain alight-emitting layer with high emission efficiency and high durability.In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPA are preferablechoices because of their excellent characteristics.

Examples of a material which can be used as a phosphorescentlight-emitting substance in the light-emitting layer 113 are as follows.

The examples include organometallic iridium complexes having 4H-triazoleskeletons, such astris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: Ir(mpptz-dmp)₃),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Mptz)₃), andtris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(iPrptz-3b)₃); organometallic iridium complexes having1H-triazole skeletons, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: Ir(Mptz1-mp)₃) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: Ir(Prptz1-Me)₃); organometallic iridium complexes havingimidazole skeletons, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: Ir(iPrpmi)₃) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: Ir(dmpimpt-Me)₃); and organometallic iridium complexes inwhich a phenylpyridine derivative having an electron-withdrawing groupis a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III) picolinate(abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C²′}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)acetylacetonate (abbreviation: FIr(acac)). These are compounds emittingblue phosphorescent light and have an emission peak at 440 nm to 520 nm.

Other examples include organometallic iridium complexes havingpyrimidine skeletons, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:Ir(mppm)₃), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₃),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)),bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ²O,O′)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(endo- and exo-mixture) (abbreviation: Ir(nbppm)₂(acac)),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(mpmppm)₂(acac)), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: Ir(dppm)₂(acac)); organometallic iridium complexes havingpyrazine skeletons, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)); organometallic iridium complexeshaving pyridine skeletons, such astris(2-phenylpyridinato-N,C²′)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C²′)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), bis(benzo[h]quinolinato)iridium(III) acetylacetonate(abbreviation: Ir(bzq)₂(acac)), tris(benzo[h]quinolinato)iridium(III)(abbreviation: Ir(bzq)₃), tris(2-phenylquinolinato-N,C²′)iridium(III)(abbreviation: Ir(pq)₃), and bis(2-phenylquinolinato-N,C²′)iridium(III)acetylacetonate (abbreviation: Ir(pq)₂(acac)); and rare earth metalcomplexes such as tris(acetylacetonato) (monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)). These are mainly compounds emittinggreen phosphorescent light and have an emission peak at 500 nm to 600nm. Note that organometallic iridium complexes having pyrimidineskeletons have distinctively high reliability and emission efficiencyand thus are especially preferable.

Other examples include organometallic iridium complexes havingpyrimidine skeletons, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: Ir(5mdppm)₂(dibm)),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(5mdppm)₂(dpm)),bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: Ir(d1npm)₂(dpm)); organometallic iridium complexes havingpyrazine skeletons, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm)), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)); organometallic iridium complexes havingpyridine skeletons, such astris(1-phenylisoquinolinato-N,C²′)iridium(III) (abbreviation: Ir(piq)₃)and bis(1-phenylisoquinolinato-N,C²′)iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)); platinum complexes such as2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato) (monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). These are compounds emitting redphosphorescent light and have an emission peak at 600 nm to 700 nm.Further, organometallic iridium complexes having pyrazine skeletons canprovide red light emission with favorable chromaticity.

As well as the above phosphorescent compounds, a variety ofphosphorescent light-emitting substances may be selected and used.

Examples of TADF materials are as follows.

The examples include a fullerene, a derivative thereof, an acridinederivative such as proflavine, eosin, or the like, and ametal-containing porphyrin such as a porphyrin containing magnesium(Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), orpalladium (Pd). Examples of the metal-containing porphyrin include aprotoporphyrin-tin fluoride complex (SnF₂(Proto IX)), amesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂(OEP)), which areshown in the following structural formulae.

Alternatively, a heterocyclic compound having a n-electron richheteroaromatic ring and a π-electron deficient heteroaromatic ring, suchas2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(PIC-TRZ) shown in the following structural formula, can be used. Theheterocyclic compound is preferably used because of the π-electron richheteroaromatic ring and the π-electron deficient heteroaromatic ring,for which the electron-transport property and the hole-transportproperty are high. Note that a substance in which the π-electron richheteroaromatic ring is directly bonded to the π-electron deficientheteroaromatic ring is particularly preferably used because the donorproperty of the π-electron rich heteroaromatic ring and the acceptorproperty of the π-electron deficient heteroaromatic ring are bothincreased and the energy difference between the S₁ level and the T₁level becomes small.

Examples of host materials in which the above-described phosphorescentlight-emitting substance or TADF material is dispersed are as follows.

The following are examples of materials having an electron-transportproperty: metal complexes such asbis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato) (4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds having polyazole skeletons, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), and2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); heterocyclic compounds having diazineskeletons, such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo quinoxaline(abbreviation: 2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine(abbreviation: 4,6mPnP2Pm), and4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); and heterocyclic compounds having pyridine skeletons,such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:35DCzPPy) and 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation:TmPyPB). Heterocyclic compounds having diazine (pyrimidine or pyrazine)skeletons have a high electron-transport property and contribute to adecrease in drive voltage.

The following are examples of materials having a hole-transportproperty: compounds having aromatic amine skeletons, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′-bis[N-(spiro-9,9′-bfluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB),4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP),4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:mBPAFLP), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP),4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF), andN-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF); compounds having carbazole skeletons, such as1,3-bis(N-carbazolyebenzene (abbreviation: mCP),4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), and3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); compounds havingthiophene skeletons, such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III), and4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV); and compounds having furan skeletons, such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II)and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II). Among the above materials, compoundshaving aromatic amine skeletons and compounds having carbazole skeletonsare preferable because these compounds are highly reliable and have highhole-transport properties to contribute to a reduction in drive voltage.

Carrier-transport materials can be selected from a variety of substancesas well as from the carrier-transport materials given above. Note thatthe host material may be a mixture of a plurality of kinds ofsubstances, and in the case of using a mixed host material, it ispreferable to mix a material having an electron-transport property witha material having a hole-transport property. By mixing the materialhaving an electron-transport property with the material having ahole-transport property, the transport property of the light-emittinglayer 113 can be easily adjusted and a recombination region can beeasily controlled. The ratio of the content of the material having ahole-transport property to the content of the material having anelectron-transport property may be 1:9 to 9:1. An exciplex may be formedby these mixed materials. It is preferable that the combination of thesematerials be selected so as to form an exciplex which exhibits lightemission whose wavelength overlaps with a wavelength of alowest-energy-side absorption band of the phosphorescent light-emittingsubstance or TADF material.

The light-emitting layer 113 having the above-described structure can beformed by co-evaporation by a vacuum evaporation method, or an inkjetmethod, a spin coating method, a dip coating method, or the like using amixed solution.

The electron-transport layer 114 contains a substance having anelectron-transport property. In this embodiment, the electron-transportlayer 114 has a structure in which the layer 114 n containing thecondensed aromatic compound or the condensed heteroaromatic compound andthe layer 114 m containing NBPhen are stacked. Since details of theselayers are described in Embodiment 1, repetition of description may beomitted. Note that as these two layers, the layer 114 n containing thecondensed aromatic compound or the condensed heteroaromatic compound isformed on the light-emitting layer 113 side and the layer 114 mcontaining NBPhen is formed on the second electrode 102 side.Furthermore, a different layer containing a substance having anelectron-transport property may be provided between the layer 114 ncontaining the condensed aromatic compound or the condensedheteroaromatic compound and the light-emitting layer 113.

It is preferable that the condensed aromatic compound or the condensedheteroaromatic compound contained in the layer 114 n be used as a hostmaterial in the light-emitting layer. Such a structure lowers a barrierto electron injection from the electron-transport layer 114 to thelight-emitting layer 113 and therefore can decrease a drive voltage ofthe light-emitting element. In this case, a light-emitting region can beregarded as being formed in the layer 114 n containing the condensedaromatic compound or the condensed heteroaromatic compound, and it canalso be said that the layer 114 n containing the condensed aromaticcompound or the condensed heteroaromatic compound contains aphosphorescent light-emitting substance (typically an iridium complex).In other words, in this structure, the layer containing NBPhen is incontact with the layer containing the condensed aromatic compound or thecondensed heteroaromatic compound, and the layer containing thecondensed aromatic compound or the condensed heteroaromatic compoundfurther contains iridium.

Alternatively, it is also possible that the layer 114 n containing thecondensed aromatic compound or the condensed heteroaromatic compounddoes not contain iridium. In such a case, the carrier-trappingproperties of the phosphorescent light-emitting substance (iridiumcomplex) do not work on the layer 114 n containing the condensedaromatic compound or the condensed heteroaromatic compound, and thelight-emitting layer 113 and the layer 114 n containing the condensedaromatic compound or the condensed heteroaromatic compound contain thesame condensed aromatic compound or condensed heteroaromatic compound.Therefore, the effect of decreasing a drive voltage is most noticeable.However, in such a case where the layer 114 n containing the condensedaromatic compound or the condensed heteroaromatic compound does notcontain iridium, the interface between the layer 114 n and a layerstacked thereover conventionally tends to have a problem with heatresistance. However, in the case where a layer containing NBPhen isstacked over the layer 114 n containing the condensed aromatic compoundor the condensed heteroaromatic compound as in the present invention,this problem can be solved without losing the effect of decreasing adrive voltage.

Between the electron-transport layer 114 and the light-emitting layer113, a layer that controls transport of electron carriers may beprovided. This is a layer formed by addition of a small amount of asubstance having a high electron-trapping property to the aforementionedmaterials having a high electron-transport property, and the layer iscapable of adjusting carrier balance by retarding transport of electroncarriers. Such a structure is very effective in preventing a problem(such as a reduction in element lifetime) caused when electrons passthrough the light-emitting layer.

In addition, the electron-injection layer 115 may be provided in contactwith the second electrode 102 between the electron-transport layer 114and the second electrode 102. For the electron-injection layer 115, analkali metal, an alkaline earth metal, or a compound thereof, such aslithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride(CaF₂), can be used. For example, a layer that is formed using asubstance having an electron-transport property and contains an alkalimetal, an alkaline earth metal, or a compound thereof can be used. Notethat a layer that is formed using a substance having anelectron-transport property and contains an alkali metal or an alkalineearth metal is preferably used as the electron-injection layer 115, inwhich case electron injection from the second electrode 102 isefficiently performed.

For the second electrode 102, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a low workfunction (specifically, a work function of 3.8 eV or less) or the likecan be used. Specific examples of such a cathode material are elementsbelonging to Groups 1 and 2 of the periodic table, such as alkali metals(e.g., lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca), andstrontium (Sr), alloys thereof (e.g., MgAg and AlLi), rare earth metalssuch as europium (Eu) and ytterbium (Yb), alloys thereof, and the like.However, when the electron-injection layer is provided between thesecond electrode 102 and the electron-transport layer, for the secondelectrode 102, any of a variety of conductive materials such as Al, Ag,ITO, or indium oxide-tin oxide containing silicon or silicon oxide canbe used regardless of the work function. Films of these electricallyconductive materials can be formed by a sputtering method, an inkjetmethod, a spin coating method, or the like.

Any of a variety of methods can be used to form the EL layer 103regardless of whether it is a dry process or a wet process. For example,a vacuum evaporation method, an inkjet method, a spin coating method, orthe like may be used. Different formation methods may be used for theelectrodes or the layers.

In addition, the electrode may be formed by a wet method using a sol-gelmethod, or by a wet method using paste of a metal material.Alternatively, the electrode may be formed by a dry method such as asputtering method or a vacuum evaporation method.

In the light-emitting element having the above-described structure,current flows due to a potential difference applied between the firstelectrode 101 and the second electrode 102, and holes and electronsrecombine in the light-emitting layer 113, so that light is emitted.

Light emission is extracted out through one or both of the firstelectrode 101 and the second electrode 102. Therefore, one or both ofthe first electrode 101 and the second electrode 102 arelight-transmitting electrodes. In the case where only the firstelectrode 101 is a light-transmitting electrode, light emission isextracted through the first electrode 101. In the case where only thesecond electrode 102 is a light-transmitting electrode, light emissionis extracted through the second electrode 102. In the case where boththe first electrode 101 and the second electrode 102 arelight-transmitting electrodes, light emission is extracted through thefirst electrode 101 and the second electrode 102.

The structure of the layers provided between the first electrode 101 andthe second electrode 102 is not limited to the above-describedstructure. Preferably, a light-emitting region where holes and electronsrecombine is positioned away from the first electrode 101 and the secondelectrode 102 so that quenching due to the proximity of thelight-emitting region and a metal used for electrodes andcarrier-injection layers can be prevented.

Further, in order that transfer of energy from an exciton generated inthe light-emitting layer can be suppressed, preferably, thehole-transport layer and the electron-transport layer which are incontact with the light-emitting layer 113, particularly acarrier-transport layer in contact with a side closer to thelight-emitting region in the light-emitting layer 113, are formed usinga substance having a wider band gap than the light-emitting substance ofthe light-emitting layer or the emission center substance included inthe light-emitting layer.

Note that this embodiment can be combined with any of the otherembodiments as appropriate.

Next, an embodiment of a light-emitting element with a structure inwhich a plurality of light-emitting units are stacked (hereinafter thistype of light-emitting element is also referred to as a stacked element)is described with reference to FIG. 1B. In this light-emitting element,a plurality of light-emitting units are provided between a firstelectrode and a second electrode. One light-emitting unit has astructure similar to that of the EL layer 103, which is illustrated inFIG. 1A. In other words, the light-emitting element illustrated in FIG.1A includes a single light-emitting unit; the light-emitting element inthis embodiment includes a plurality of light-emitting units.

In FIG. 1B, a first light-emitting unit 511 and a second light-emittingunit 512 are stacked between a first electrode 501 and a secondelectrode 502, and a charge-generation layer 513 is provided between thefirst light-emitting unit 511 and the second light-emitting unit 512.The first electrode 501 and the second electrode 502 correspond,respectively, to the first electrode 101 and the second electrode 102illustrated in FIG. 1A, and the materials given in the description forFIG. 1A can be used. Further, the first light-emitting unit 511 and thesecond light-emitting unit 512 may have the same structure or differentstructures.

The charge-generation layer 513 includes a composite material of anorganic compound and a metal oxide. As the composite material of theorganic compound and the metal oxide, the composite material which canbe used for the hole-injection layer 111 illustrated in FIG. 1A can beused. Note that when the anode side of a light-emitting unit is incontact with a charge-generation layer, the charge-generation layer canalso serve as a hole-injection layer of the light-emitting unit; thus, ahole-injection layer does not need to be formed in the light-emittingunit.

The charge-generation layer 513 may have a stacked-layer structure of alayer containing a composite material of an organic compound and a metaloxide and a layer containing another material. For example, a layercontaining a composite material of an organic compound and a metal oxidemay be combined with a layer containing a compound of a substanceselected from substances with an electron-donating property and acompound with a high electron-transport property. Moreover, a layercontaining a composite material of an organic compound and a metal oxidemay be combined with a transparent conductive film.

An electron-injection buffer layer may be provided between thecharge-generation layer 513 and the light-emitting unit on the anodeside of the charge-generation layer. The electron-injection buffer layeris formed by stacking a very thin film of an alkali metal and anelectron-relay layer containing a substance having an electron-transportproperty. The very thin film of the alkali metal corresponds to theelectron-injection layer 115 and has a function of lowering an electroninjection barrier. The electron-relay layer has a function of preventingan interaction between the film of the alkali metal and thecharge-generation layer and smoothly transferring electrons.

As the substance having an electron-transport property which iscontained in the electron-relay layer of the electron-injection bufferlayer, it is preferable to select a substance having a LUMO levelbetween the LUMO level of the substance having an acceptor propertywhich is contained in the charge-generation layer 513 in contact withthe electron-injection buffer layer and the LUMO level of a substance(NBPhen) contained in the layer containing NBPhen in contact with theelectron-injection buffer layer. Specifically, the LUMO level of thesubstance having an electron-transport property which is contained inthe electron-relay layer is preferably higher than or equal to −5.0 eV,more preferably higher than or equal to −5.0 eV and lower than or equalto −3.0 eV. Note that as the substance having an electron-transportproperty in an electron-injection buffer region, a phthalocyanine-basedmaterial or a metal complex having a metal-oxygen bond and an aromaticligand is preferably used.

In the case where the electron-injection buffer layer is formed, thefilm of the alkali metal of the electron-injection buffer layer servesas the electron-injection layer in the light-emitting unit on the anodeside; therefore, the light-emitting unit does not further need anelectron-injection layer.

In the case where the above-described film of the alkali metal is a filmcontaining lithium, crosstalk between adjacent pixels can be suppressedin a display device including light-emitting elements having the abovestructure. Accordingly, the display device can provide remarkablyhigh-quality images and videos.

The light-emitting element having two light-emitting units is describedwith reference to FIG. 1B; however, the present invention can besimilarly applied to a light-emitting element in which three or morelight-emitting units are stacked. With a plurality of light-emittingunits partitioned by the charge-generation layer between a pair ofelectrodes as in the light-emitting element according to thisembodiment, it is possible to provide a light-emitting element which canemit light with high luminance with the current density kept low and hasa long lifetime. Moreover, a light-emitting device having low powerconsumption, which can be driven at low voltage, can be achieved.

Further, when emission colors of light-emitting units are madedifferent, light emission of a desired color can be provided from thelight-emitting element as a whole. For example, in a light-emittingelement having two light-emitting units, the emission colors of thefirst light-emitting unit may be red and green and the emission color ofthe second light-emitting unit may be blue, so that the light-emittingelement can emit white light as the whole element.

The above-described structure can be combined with any of the structuresin this embodiment and the other embodiments.

The light-emitting element having the above structure in this embodimenthas high heat resistance. In particular, a light-emitting element havinga structure in which a layer containing a condensed heteroaromaticcompound and a layer containing NBPhen are stacked is highly usefulbecause not only a luminance decrease but also a voltage decrease can besuppressed in measurement of characteristics before and after ahigh-temperature exposition test.

Embodiment 3

In this embodiment, a different embodiment of the present invention isdescribed. In the light-emitting element described in Embodiment 1 or 2,NBPhen is used for a layer on the cathode side (the layer 114 mcontaining NBPhen) in the electron-transport layer 114.

It is preferable that the concentration of impurities in NBPhen,particularly the concentration of NBPhen derivatives mono-substituted bychlorine, be low, in which case a highly reliable light-emitting elementcan be provided.

The impurity concentration of a material used for the EL layer 103normally has an insignificant influence on a layer positioned apart fromthe light-emitting layer 113. However, the concentration of impuritiesin NBPhen solid (particularly the concentration of NBPhen derivativesmono-substituted by chlorine) has an influence on the reliability of alight-emitting element even when NBPhen exists apart from thelight-emitting layer 113. Therefore, in a light-emitting elementincluding NBPhen, the concentration of impurities (particularly NBPhenderivatives mono-substituted by chlorine) is preferably low.Specifically, with the use of a material in which the amount of chlorinein NBPhen is 100 ppm or less for a light-emitting element, deteriorationof the light-emitting element can be minimized, so that a highlyreliable light-emitting element can be obtained. Meanwhile, the impurityconcentration indicates the chlorine concentration in 100 μL of theabsorption solution for 1 g of NBPhen solid measured by combustion ionchromatography. Therefore, the above impurity concentration isequivalent to a chlorine concentration in NBPhen solid of 1.0×10⁻² g/kg,and is equivalent to a concentration of a chlorine mono-substitutedderivative in NBPhen solid of 1.7×10⁻¹ g/kg.

Note that in order to achieve the effect of improving reliability, thelayer 114 n containing the condensed aromatic compound or the condensedheteroaromatic compound in the light-emitting element described inEmbodiment 1 or 2 may include any kind of material. In other words, thelayer 114 n containing the condensed aromatic compound or the condensedheteroaromatic compound does not necessarily include the condensedaromatic compound or the condensed heteroaromatic compound, and a givenelectron-transport material can be used. In that case, the layer 114 ncontaining the condensed aromatic compound or the condensedheteroaromatic compound may be described as a first electron-transportlayer 114 n.

As described above, the light-emitting element of this embodimentincludes at least the pair of electrodes (the first electrode 101 andthe second electrode 102) and the EL layer 103 including thelight-emitting layer 113 and the electron-transport layer 114 containingNBPhen, and the amount of chlorine in NBPhen contained in theelectron-transport layer 114 is less than or equal to 100 ppm. Thelight-emitting element includes at least the pair of electrodes (thefirst electrode 101 and the second electrode 102) and the EL layer 103including the light-emitting layer 113 and the electron-transport layer114 including the first electron-transport layer 114 n and the layer 114m containing NBPhen, and the amount of chlorine in NBPhen contained inthe layer 114 m is less than or equal to 100 ppm. Alternatively, thelight-emitting element includes at least the pair of electrodes (thefirst electrode 101 and the second electrode 102) and the EL layer 103including the light-emitting layer 113 and the electron-transport layer114 including the layer 114 m containing NBPhen formed apart from thelight-emitting layer 113, and the amount of chlorine in NBPhen containedin the layer 114 m is less than or equal to 100 ppm. Such alight-emitting element has high reliability. Here, the above impurityconcentration corresponds to a value obtained by the aforementionedmeasurement.

Note that NBPhen with a chlorine content of 100 ppm or less is also anembodiment of the present invention. In particular, NBPhen with thecontent of chlorine derived from the chlorine mono-substituted compoundbeing less than or equal to 100 ppm is an embodiment of the presentinvention. Here, the impurity concentration corresponds to a valueobtained by the aforementioned measurement

Embodiment 4

In this embodiment, a light-emitting device including the light-emittingelement described in any of Embodiments 1 to 3 is described.

In this embodiment, the light-emitting device manufactured using thelight-emitting element described in any of Embodiments 1 to 3 isdescribed with reference to FIGS. 2A and 2B. Note that FIG. 2A is a topview of the light-emitting device and FIG. 2B is a cross-sectional viewtaken along the lines A-B and C-D in FIG. 2A. This light-emitting deviceincludes a driver circuit portion (source line driver circuit) 601, apixel portion 602, and a driver circuit portion (gate line drivercircuit) 603, which are to control light emission of a light-emittingelement and illustrated with dotted lines. Reference numeral 604 denotesa sealing substrate; 605, a sealing material; and 607, a spacesurrounded by the sealing material 605.

Reference numeral 608 denotes a wiring for transmitting signals to beinput to the source line driver circuit 601 and the gate line drivercircuit 603 and receiving signals such as a video signal, a clocksignal, a start signal, and a reset signal from an FPC (flexible printedcircuit) 609 serving as an external input terminal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The light-emitting device in the present specificationincludes, in its category, not only the light-emitting device itself butalso the light-emitting device provided with the FPC or the PWB.

Next, a cross-sectional structure will be described with reference toFIG. 2B. The driver circuit portion and the pixel portion are formedover an element substrate 610; FIG. 2B shows the source line drivercircuit 601, which is a driver circuit portion, and one of the pixels inthe pixel portion 602.

As the source line driver circuit 601, a CMOS circuit in which ann-channel FET 623 and a p-channel FET 624 are combined is formed. Inaddition, the driver circuit may be formed with any of a variety ofcircuits such as a CMOS circuit, a PMOS circuit, or an NMOS circuit.Although a driver integrated type in which the driver circuit is formedover the substrate is illustrated in this embodiment, the driver circuitis not necessarily formed over the substrate, and the driver circuit canbe formed outside, not over the substrate.

The pixel portion 602 includes a plurality of pixels including aswitching FET 611, a current controlling FET 612, and a first electrode613 electrically connected to a drain of the current controlling FET612. Note that to cover an end portion of the first electrode 613, aninsulator 614 is formed, for which a positive photosensitive acrylicresin film is used here.

In order to improve coverage, the insulator 614 is formed to have acurved surface with curvature at its upper or lower end portion. Forexample, in the case where positive photosensitive acrylic is used for amaterial of the insulator 614, only the upper end portion of theinsulator 614 preferably has a curved surface with a curvature radius(0.2 μm to 3 μm). As the insulator 614, either a negative photosensitiveresin or a positive photosensitive resin can be used.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. Here, as a material used for the first electrode 613functioning as an anode, a material having a high work function ispreferably used. For example, a single-layer film of an ITO film, anindium tin oxide film containing silicon, an indium oxide filmcontaining zinc oxide at 2 wt % to 20 wt %, a titanium nitride film, achromium film, a tungsten film, a Zn film, a Pt film, or the like, astack of a titanium nitride film and a film containing aluminum as itsmain component, a stack of three layers of a titanium nitride film, afilm containing aluminum as its main component, and a titanium nitridefilm, or the like can be used. The stacked-layer structure enables lowwiring resistance, favorable ohmic contact, and a function as an anode.

The EL layer 616 is formed by any of a variety of methods such as anevaporation method using an evaporation mask, an inkjet method, and aspin coating method. The EL layer 616 has the structure described in anyof Embodiments 1 to 3.

As a material used for the second electrode 617, which is formed overthe EL layer 616 and functions as a cathode, a material having a lowwork function (e.g., Al, Mg, Li, and Ca, or an alloy or a compoundthereof, such as MgAg, MgIn, and AlLi) is preferably used. In the casewhere light generated in the EL layer 616 is transmitted through thesecond electrode 617, a transparent conductive film (e.g., ITO, indiumoxide containing zinc oxide at 2 wt % to 20 wt %, indium tin oxidecontaining silicon, or zinc oxide (ZnO)) or a stack of a thin metal filmand a transparent conductive film is preferably used for the secondelectrode 617.

Note that the light-emitting element is formed with the first electrode613, the EL layer 616, and the second electrode 617. The light-emittingelement has the structure described in any of Embodiments 1 to 3. In thelight-emitting device of this embodiment, the pixel portion, whichincludes a plurality of light-emitting elements, may include both thelight-emitting element described in any of Embodiments 1 to 3 and alight-emitting element having a different structure.

The sealing substrate 604 is attached to the element substrate 610 withthe sealing material 605, so that a light-emitting element 618 isprovided in the space 607 surrounded by the element substrate 610, thesealing substrate 604, and the sealing material 605. The space 607 maybe filled with filler, or may be filled with an inert gas (such asnitrogen or argon), or the sealing material 605. It is preferable thatthe sealing substrate be provided with a recessed portion and a dryingagent be provided in the recessed portion, in which case deteriorationdue to influence of moisture can be suppressed.

An epoxy-based resin or glass frit is preferably used for the sealingmaterial 605. It is preferable that such a material do not transmitmoisture or oxygen as much as possible. As the sealing substrate 604, aglass substrate, a quartz substrate, or a plastic substrate formed offiber reinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester,and acrylic can be used.

As described above, the light-emitting device which uses thelight-emitting element described in any of Embodiments 1 to 3 can beobtained.

The light-emitting device in this embodiment is fabricated using thelight-emitting element described in any of Embodiments 1 to 3 and thuscan have favorable characteristics. Specifically, since thelight-emitting element described in any of Embodiments 1 to 3 has highheat resistance, the light-emitting device can have high heatresistance. Alternatively, the light-emitting element described in anyof Embodiments 1 to 3 has high reliability, the light-emitting devicecan have high reliability.

FIGS. 3A and 3B each illustrate an example of a light-emitting device inwhich full color display is achieved by formation of a light-emittingelement exhibiting white light emission and with the use of coloringlayers (color filters) and the like. In FIG. 3A, a substrate 1001, abase insulating film 1002, a gate insulating film 1003, gate electrodes1006, 1007, and 1008, a first interlayer insulating film 1020, a secondinterlayer insulating film 1021, a peripheral portion 1042, a pixelportion 1040, a driver circuit portion 1041, first electrodes 1024W,1024R, 1024G and 1024B of light-emitting elements, a partition 1025, anEL layer 1028, a second electrode 1029 of the light-emitting elements, asealing substrate 1031, a sealing material 1032, and the like areillustrated.

In FIG. 3A, coloring layers (a red coloring layer 1034R, a greencoloring layer 1034G, and a blue coloring layer 1034B) are provided on atransparent base material 1033. A black layer (a black matrix) 1035 maybe additionally provided. The transparent base material 1033 providedwith the coloring layers and the black layer is positioned and fixed tothe substrate 1001. Note that the coloring layers and the black layerare covered with an overcoat layer 1036. In FIG. 3A, light emitted frompart of the light-emitting layer does not pass through the coloringlayers, while light emitted from the other part of the light-emittinglayer passes through the coloring layers. Since light which does notpass through the coloring layers is white and light which passes throughany one of the coloring layers is red, blue, or green, an image can bedisplayed using pixels of the four colors.

FIG. 3B illustrates an example in which the coloring layers (the redcoloring layer 1034R, the green coloring layer 1034G and the bluecoloring layer 1034B) are provided between the gate insulating film 1003and the first interlayer insulating film 1020. As in the structure, thecoloring layers may be provided between the substrate 1001 and thesealing substrate 1031.

The above-described light-emitting device is a light-emitting devicehaving a structure in which light is extracted from the substrate 1001side where the FETs are formed (a bottom emission structure), but may bea light-emitting device having a structure in which light is extractedfrom the sealing substrate 1031 side (a top emission structure). FIG. 4is a cross-sectional view of a light-emitting device having a topemission structure. In this case, a substrate which does not transmitlight can be used as the substrate 1001. The process up to the step offorming a connection electrode which connects the FET and the anode ofthe light-emitting element is performed in a manner similar to that ofthe light-emitting device having a bottom emission structure. Then, athird interlayer insulating film 1037 is formed to cover an electrode1022. This insulating film may have a planarization function. The thirdinterlayer insulating film 1037 can be formed using a material similarto that of the second interlayer insulating film, and can alternativelybe formed using any of other various materials.

The first electrodes 1024W, 1024R, 1024G and 1024B of the light-emittingelements each serve as an anode here, but may serve as a cathode.Further, in the case of a light-emitting device having a top emissionstructure as illustrated in FIG. 4, the first electrodes are preferablyreflective electrodes. The EL layer 1028 is formed to have a structuresimilar to the structure of the EL layer 103, which is described in anyof Embodiments 1 to 3, with which white light emission can be obtained.

In the case of a top emission structure as illustrated in FIG. 4,sealing can be performed with the sealing substrate 1031 on which thecoloring layers (the red coloring layer 1034R, the green coloring layer1034G, and the blue coloring layer 1034B) are provided. The sealingsubstrate 1031 may be provided with the black layer (black matrix) 1035which is positioned between pixels. The coloring layers (the redcoloring layer 1034R, the green coloring layer 1034G and the bluecoloring layer 1034B) and the black layer (black matrix) may be coveredwith an overcoat layer. Note that a light-transmitting substrate is usedas the sealing substrate 1031.

Although an example in which full color display is performed using fourcolors of red, green, blue, and white is shown here, there is noparticular limitation and full color display using three colors of red,green, and blue or four colors of red, yellow, green, and blue may beperformed.

The light-emitting device in this embodiment is fabricated using thelight-emitting element described in any of Embodiments 1 to 3 and thuscan have favorable characteristics. Specifically, since thelight-emitting element described in any of Embodiments 1 to 3 has highheat resistance, the light-emitting device can have high reliability.

An active matrix light-emitting device is described above, whereas apassive matrix light-emitting device is described below. FIGS. 5A and 5Billustrate a passive matrix light-emitting device manufactured using thepresent invention. FIG. 5B is a cross-sectional view taken along theline X-Y in FIG. 5A. In FIGS. 5A and 5B, over a substrate 951, an ELlayer 955 is provided between an electrode 952 and an electrode 956. Anend portion of the electrode 952 is covered with an insulating layer953. A partition layer 954 is provided over the insulating layer 953.The sidewalls of the partition layer 954 are aslope such that thedistance between both sidewalls is gradually narrowed toward the surfaceof the substrate. In other words, a cross section taken along thedirection of the short side of the partition layer 954 is trapezoidal,and the lower side (a side in contact with the insulating layer 953,which is one of a pair of parallel sides of the trapezoidal crosssection) is shorter than the upper side (a side not in contact with theinsulating layer 953, which is the other one of the pair of parallelsides). The partition layer 954 thus provided can prevent defects in thelight-emitting element due to static electricity or others. Thepassive-matrix light-emitting device also includes the light-emittingelement with high heat resistance described in any of Embodiments 1 to3; thus, the light-emitting device can have high reliability.

Since many minute light-emitting elements arranged in a matrix in thelight-emitting device described above can each be controlled, thelight-emitting device can be suitably used as a display device fordisplaying images.

This embodiment can be freely combined with any of other embodiments.

Embodiment 5

In this embodiment, an example in which the light-emitting elementdescribed in any of Embodiments 1 to 3 is used for a lighting devicewill be described with reference to FIGS. 6A and 6B. FIG. 6B is a topview of the lighting device, and FIG. 6A is a cross-sectional view takenalong the line e-f in FIG. 6B.

In the lighting device in this embodiment, a first electrode 401 isformed over a substrate 400 which is a support and has alight-transmitting property. The first electrode 401 corresponds to thefirst electrode 101 in Embodiment 1. When light is extracted through thefirst electrode 401 side, the first electrode 401 is formed using amaterial having a light-transmitting property.

A pad 412 for applying voltage to a second electrode 404 is providedover the substrate 400.

An EL layer 403 is formed over the first electrode 401. The structure ofthe EL layer 403 corresponds to, for example, the structure of the ELlayer 103 in Embodiment 1, or the structure in which the light-emittingunits 511 and 512 and the charge-generation layer 513 are combined.Refer to the descriptions for the structure.

The second electrode 404 is formed to cover the EL layer 403. The secondelectrode 404 corresponds to the second electrode 102 in Embodiment 1.The second electrode 404 is formed using a material having highreflectance when light is extracted through the first electrode 401side. The second electrode 404 is connected to the pad 412, wherebyvoltage is applied.

As described above, the lighting device described in this embodimentincludes a light-emitting element including the first electrode 401, theEL layer 403, and the second electrode 404. Since the light-emittingelement is a light-emitting element with high emission efficiency, thelighting device in this embodiment can be a lighting device having lowpower consumption.

The light-emitting element having the above structure is fixed to asealing substrate 407 with sealing materials 405 and 406 and sealing isperformed, whereby the lighting device is completed. It is possible touse only either the sealing material 405 or the sealing material 406.The inner sealing material 406 (not shown in FIG. 6B) can be mixed witha desiccant which enables moisture to be adsorbed, increasingreliability.

When parts of the pad 412 and the first electrode 401 are extended tothe outside of the sealing materials 405 and 406, the extended parts canserve as external input terminals. An IC chip 420 mounted with aconverter or the like may be provided over the external input terminals.

The lighting device described in this embodiment includes as an ELelement the light-emitting element with high heat resistance describedin any of Embodiments 1 to 3; thus, the lighting device can have highreliability.

Embodiment 6

In this embodiment, examples of electronic devices each including thelight-emitting element described in any of Embodiments 1 to 3 will bedescribed. The light-emitting element described in any of Embodiments 1to 3 has high heat resistance and high reliability. As a result, theelectronic devices described in this embodiment can each include adisplay portion having high reliability.

Examples of the electronic device to which the above light-emittingelement is applied include television devices (also referred to as TV ortelevision receivers), monitors for computers and the like, cameras suchas digital cameras and digital video cameras, digital photo frames,mobile phones (also referred to as cell phones or mobile phone devices),portable game machines, portable information terminals, audio playbackdevices, large game machines such as pachinko machines, and the like.Specific examples of these electronic devices are given below.

FIG. 7A illustrates an example of a television device. In the televisiondevice, a display portion 7103 is incorporated in a housing 7101. Here,the housing 7101 is supported by a stand 7105. Images can be displayedon the display portion 7103, and in the display portion 7103, thelight-emitting elements described in any of Embodiments 1 to 3 arearranged in a matrix.

Operation of the television device can be performed with an operationswitch of the housing 7101 or a separate remote controller 7110. Withoperation keys 7109 of the remote controller 7110, channels and volumecan be controlled and images displayed on the display portion 7103 canbe controlled. The remote controller 7110 may be provided with a displayportion 7107 for displaying data output from the remote controller 7110.

Note that the television device is provided with a receiver, a modem,and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 7B1 illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer is manufactured by arranging light-emitting elementssimilar to those described in any of Embodiments 1 to 3 in a matrix inthe display portion 7203. The computer illustrated in FIG. 7B1 may havea structure illustrated in FIG. 7B2. The computer illustrated in FIG.7B2 is provided with a second display portion 7210 instead of thekeyboard 7204 and the pointing device 7206. The second display portion7210 has a touch screen, and input can be performed by operation ofimages, which are displayed on the second display portion 7210, with afinger or a dedicated pen. The second display portion 7210 can alsodisplay images other than the display for input. The display portion7203 may also have a touch screen. Connecting the two screens with ahinge so that the computer becomes foldable can prevent troubles; forexample, the screens can be prevented from being cracked or broken whilethe computer is being stored or carried.

FIG. 7C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be folded. Thehousing 7301 incorporates a display portion 7304 including thelight-emitting elements described in any of Embodiments 1 to 3 andarranged in a matrix, and the housing 7302 incorporates a displayportion 7305. In addition, the portable game machine illustrated in FIG.7C includes a speaker portion 7306, a recording medium insertion portion7307, an LED lamp 7308, input means (an operation key 7309, a connectionterminal 7310, a sensor 7311 (a sensor having a function of measuring orsensing force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, or infrared rays), and a microphone 7312),and the like. Needless to say, the structure of the portable gamemachine is not limited to the above as long as the display portion whichincludes the light-emitting elements described in any of Embodiments 1to 3 and arranged in a matrix is used as either the display portion 7304or the display portion 7305, or both, and the structure can includeother accessories as appropriate. The portable game machine illustratedin FIG. 7C has a function of reading out a program or data stored in arecoding medium to display it on the display portion, and a function ofsharing information with another portable game machine by wirelesscommunication. Note that functions of the portable game machineillustrated in FIG. 7C are not limited to them, and the portable gamemachine can have various functions.

FIG. 7D illustrates an example of a mobile phone. The mobile phone isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone hasthe display portion 7402 including the light-emitting elements describedin any of Embodiments 1 to 3 and arranged in a matrix.

When the display portion 7402 of the mobile phone illustrated in FIG. 7Dis touched with a finger or the like, data can be input into the mobilephone. In this case, operations such as making a call and creating ane-mail can be performed by touching the display portion 7402 with afinger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are combined.

For example, in the case of making a call or creating an e-mail, acharacter input mode is selected for the display portion 7402 so thatcharacters displayed on a screen can be input. In this case, it ispreferable to display a keyboard or number buttons on almost the entirescreen of the display portion 7402.

When a sensing device including a sensor such as a gyroscope or anacceleration sensor for detecting inclination is provided inside themobile phone, display on the screen of the display portion 7402 can beautomatically changed in direction by determining the orientation of themobile phone (whether the mobile phone is placed horizontally orvertically).

The screen modes are switched by touch on the display portion 7402 oroperation with the operation buttons 7403 of the housing 7401. Thescreen modes can be switched depending on the kind of images displayedon the display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by thedisplay portion 7402 while in touch with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits a near-infrared light inthe display portion, an image of a finger vein, or a palm vein can betaken.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 5 asappropriate.

As described above, the application range of the light-emitting deviceincluding the light-emitting element described in any of Embodiments 1to 3 is wide so that this light-emitting device can be applied toelectronic devices in a variety of fields. By using the light-emittingelement described in any of Embodiments 1 to 3, an electronic devicehaving high heat resistance and high reliability can be obtained.

FIG. 8 illustrates an example of a liquid crystal display device usingthe light-emitting element described in any of Embodiments 1 to 3 for abacklight. The liquid crystal display device illustrated in FIG. 8includes a housing 901, a liquid crystal layer 902, a backlight unit903, and a housing 904. The liquid crystal layer 902 is connected to adriver IC 905. The light-emitting element described in any ofEmbodiments 1 to 3 is used for the backlight unit 903, to which currentis supplied through a terminal 906.

The light-emitting element described in any of Embodiments 1 to 3 isused for the backlight of the liquid crystal display device; thus, thebacklight can have reduced power consumption. In addition, the use ofthe light-emitting element described in Embodiment 2 enables manufactureof a planar-emission lighting device and further a larger-areaplanar-emission lighting device; therefore, the backlight can be alarger-area backlight, and the liquid crystal display device can also bea larger-area device. Furthermore, the light-emitting device includingthe light-emitting element described in Embodiment 2 can be thinner thana conventional one; accordingly, the display device can also be thinner.

FIG. 9 illustrates an example in which the light-emitting elementdescribed in any of Embodiments 1 to 3 is used for a table lamp which isa lighting device. The table lamp illustrated in FIG. 9 includes ahousing 2001 and a light source 2002, and the lighting device describedin Embodiment 5 is used for the light source 2002.

FIG. 10 illustrates an example in which the light-emitting elementdescribed in any of Embodiments 1 to 3 is used for an indoor lightingdevice 3001. Since the light-emitting element described in any ofEmbodiments 1 to 3 has high heat resistance, the lighting device canhave high reliability. Further, since the light-emitting elementdescribed in any of Embodiments 1 to 3 can have a large area, thelight-emitting element can be used for a large-area lighting device.Furthermore, since the light-emitting element described in any ofEmbodiments 1 to 3 is thin, the light-emitting element can be used for alighting device having a reduced thickness.

The light-emitting element described in any of Embodiments 1 to 3 canalso be used for an automobile windshield or an automobile dashboard.FIG. 11 illustrates one mode.

A display region 5000 and a display region 5001 are display devicesprovided in the automobile windshield in which the light-emittingelements described in any of Embodiments 1 to 3 are incorporated. Thelight-emitting elements described in any of Embodiments 1 to 3 can beformed into what is called a see-through display device, through whichthe opposite side can be seen, by including a first electrode and asecond electrode formed of electrodes having light-transmittingproperties. Such see-through display devices can be provided even in theautomobile windshield, without hindering the vision. Note that in thecase where a driving transistor or the like is provided, a transistorhaving a light-transmitting property, such as an organic transistorusing an organic semiconductor material or a transistor using an oxidesemiconductor, is preferably used.

A display region 5002 is a display device provided in a pillar portionin which the light-emitting elements described in any of Embodiments 1to 3 are incorporated. The display region 5002 can compensate for theview hindered by the pillar portion by showing an image taken by animaging unit provided in the car body. Similarly, a display region 5003provided in the dashboard can compensate for the view hindered by thecar body by showing an image taken by an imaging unit provided in theoutside of the car body, which leads to elimination of blind areas andenhancement of safety. Showing an image so as to compensate for the areawhich a driver cannot see makes it possible for the driver to confirmsafety easily and comfortably.

A display region 5004 and a display region 5005 can provide a variety ofkinds of information such as navigation data, a speedmeter, atachometer, a mileage, a fuel level, a gearshift state, andair-condition setting. The content of the display can be freely changedby a user as appropriate. Note that such information can also be shownby the display regions 5000 to 5003. The display regions 5000 to 5005can also be used as lighting devices.

The light-emitting element described in any of Embodiments 1 to 3 hashigh heat resistance. Accordingly, the light-emitting element describedin any of Embodiments 1 to 3 can be suitably used for an in-vehiclelight-emitting device or lighting device which is to be placed in a veryhigh-temperature environment in midsummer or the like.

FIGS. 12A and 12B illustrate an example of a foldable tablet terminal.FIG. 12A illustrates the tablet terminal which is unfolded. The tabletterminal includes a housing 9630, a display portion 9631 a, a displayportion 9631 b, a display mode switch 9034, a power switch 9035, apower-saving mode switch 9036, and a clasp 9033. Note that in the tabletterminal, one or both of the display portion 9631 a and the displayportion 9631 b is/are formed using a light-emitting device whichincludes the light-emitting element described in any of Embodiments 1 to3.

Part of the display portion 9631 a can be a touchscreen region 9632 aand data can be input when a displayed operation key 9637 is touched.Although half of the display portion 9631 a has only a display functionand the other half has a touchscreen function, one embodiment of thepresent invention is not limited to the structure. The whole displayportion 9631 a may have a touchscreen function. For example, a keyboardcan be displayed on the entire region of the display portion 9631 a sothat the display portion 9631 a is used as a touchscreen, and thedisplay portion 9631 b can be used as a display screen.

Like the display portion 9631 a, part of the display portion 9631 b canbe a touchscreen region 9632 b. When a switching button 9639 forshowing/hiding a keyboard on the touchscreen is touched with a finger, astylus, or the like, the keyboard can be displayed on the displayportion 9631 b.

Touch input can be performed in the touchscreen region 9632 a and thetouchscreen region 9632 b at the same time.

The display mode switch 9034 can switch the display between portraitmode, landscape mode, and the like, and between monochrome display andcolor display, for example. The power-saving mode switch 9036 cancontrol display luminance in accordance with the amount of externallight in use of the tablet terminal sensed by an optical sensorincorporated in the tablet terminal. Another sensing device including asensor such as a gyroscope or an acceleration sensor for sensinginclination may be incorporated in the tablet terminal, in addition tothe optical sensor.

Although FIG. 12A illustrates an example in which the display portion9631 a and the display portion 9631 b have the same display area, oneembodiment of the present invention is not limited to the example. Thedisplay portion 9631 a and the display portion 9631 b may have differentdisplay areas and different display quality. For example, higherdefinition images may be displayed on one of the display portions 9631 aand 9631 b.

FIG. 12B illustrates the tablet terminal which is folded. The tabletterminal in this embodiment includes the housing 9630, a solar cell9633, a charge and discharge control circuit 9634, a battery 9635, and aDCDC converter 9636. In FIG. 12B, a structure including the battery 9635and the DCDC converter 9636 is illustrated as an example of the chargeand discharge control circuit 9634.

Since the tablet terminal is foldable, the housing 9630 can be closedwhen the tablet terminal is not in use. As a result, the display portion9631 a and the display portion 9631 b can be protected, therebyproviding a tablet terminal with high endurance and high reliability forlong-term use.

The tablet terminal illustrated in FIGS. 12A and 12B can have otherfunctions such as a function of displaying various kinds of data (e.g.,a still image, a moving image, and a text image), a function ofdisplaying a calendar, a date, the time, or the like on the displayportion, a touch-input function of operating or editing the datadisplayed on the display portion by touch input, and a function ofcontrolling processing by various kinds of software (programs).

The solar cell 9633 provided on a surface of the tablet terminal cansupply power to the touchscreen, the display portion, a video signalprocessing portion, or the like. Note that a structure in which thesolar cell 9633 is provided on one or both surfaces of the housing 9630is preferable because the battery 9635 can be charged efficiently.

The structure and operation of the charge and discharge control circuit9634 illustrated in FIG. 12B will be described with reference to a blockdiagram of FIG. 12C. FIG. 12C illustrates the solar cell 9633, thebattery 9635, the DCDC converter 9636, a converter 9638, switches SW1 toSW3, and a display portion 9631. The battery 9635, the DCDC converter9636, the converter 9638, and the switches SW1 to SW3 correspond to thecharge and discharge control circuit 9634 illustrated in FIG. 12B.

First, description is made on an example of the operation in the casewhere power is generated by the solar cell 9633 with the use of externallight. The voltage of the power generated by the solar cell is raised orlowered by the DCDC converter 9636 so as to be voltage for charging thebattery 9635. Then, when power from the solar cell 9633 is used for theoperation of the display portion 9631, the switch SW1 is turned on andthe voltage of the power is raised or lowered by the converter 9638 soas to be voltage needed for the display portion 9631. When images arenot displayed on the display portion 9631, the switch SW1 is turned offand the switch SW2 is turned on so that the battery 9635 is charged.

Although the solar cell 9633 is described as an example of a powergeneration means, the power generation means is not particularlylimited, and the battery 9635 may be charged by another power generationmeans such as a piezoelectric element or a thermoelectric conversionelement (Peltier element). The battery 9635 may be charged by anon-contact power transmission module capable of performing charging bytransmitting and receiving power wirelessly (without contact), or any ofthe other charge means used in combination, and the power generationmeans is not necessarily provided.

One embodiment of the present invention is not limited to the tabletterminal having the shape illustrated in FIGS. 12A to 12C as long as thedisplay portion 9631 is included.

Example 1

In this example, light-emitting elements (light-emitting elements 1 to3) of one embodiment of the present invention and comparativelight-emitting elements (comparative light-emitting elements 1 to 3)will be described. Structure formulae of organic compounds used in thelight-emitting elements 1 to 3 and the comparative light-emittingelements 1 to 3 are shown below.

Methods for manufacturing the light-emitting elements 1 to 3 and thecomparative light-emitting elements 1 to 3 of this example will bedescribed below.

(Method for Manufacturing Light-Emitting Element 1)

First, a film of indium tin oxide containing silicon oxide (ITSO) wasformed over a glass substrate by a sputtering method, so that the firstelectrode 101 was formed. The thickness thereof was 110 nm and theelectrode area was 2 mm×2 mm. Here, the first electrode 101 functions asan anode of the light-emitting element.

Next, as pretreatment for forming the light-emitting element over thesubstrate, UV-ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for one hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate was cooled down for about 30 minutes.

Then, the substrate over which the first electrode 101 was formed wasfixed to a substrate holder provided in the vacuum evaporation apparatusso that the surface on which the first electrode 101 was formed faceddownward. The pressure in the vacuum evaporation apparatus was reducedto about 10⁻⁴ Pa. After that, over the first electrode 101,4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II) represented by Structural Formula (i) and molybdenum(VI) oxidewere deposited by co-evaporation by an evaporation method usingresistance heating, so that the hole-injection layer 111 was formed. Thethickness of the hole-injection layer 111 was set to 30 nm, and theweight ratio of DBT3P-II to molybdenum oxide was adjusted to 1:0.5(=DBT3P-II: molybdenum oxide). Note that the co-evaporation methodrefers to an evaporation method in which evaporation is carried out froma plurality of evaporation sources at the same time in one treatmentchamber.

Next, a film of 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP) which is represented by Structural Formula (ii)was formed to a thickness of 20 nm over the hole-injection layer 111 toform the hole-transport layer 112.

Further, over the hole-transport layer 112, the light-emitting layer 113was formed by co-evaporation of2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) represented by Structural Formula (iii),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-cabazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF) represented by Structural Formula (iv), andbis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-P)₂(dibm)]) represented by Structural Formula(v) with a weight ratio of 0.8:0.2:0.06(=2mDBTBPDBq-II:PCBBiF:[Ir(dmdppr-P)₂(dibm)]) to a thickness of 40 nm.

Then, the electron-transport layer 114 was formed over thelight-emitting layer 113 in such a manner that a 20 nm thick film of2mDBTBPDBq-II was formed (the layer 114 n containing the condensedaromatic compound or the condensed heteroaromatic compound) and a 20 nmthick film of 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline(abbreviation: NBPhen) represented by Structural Formula (vi) was formed(the layer containing NBPhen).

After the formation of the electron-transport layer 114, lithiumfluoride (LiF) was deposited by evaporation to a thickness of 1 nm, sothat the electron-injection layer 115 was formed. Lastly, aluminum wasdeposited by evaporation to a thickness of 200 nm to form the secondelectrode 102 functioning as a cathode. Thus, the light-emitting element1 in this example was fabricated.

(Method for Manufacturing Comparative Light-Emitting Element 1)

The comparative light-emitting element 1 was manufactured in the samemanner as the light-emitting element 1 except for usingbathophenanthroline (abbreviation: BPhen) represented by StructuralFormula (xi) instead of NBPhen.

(Method for Manufacturing Light-Emitting Element 2)

The light-emitting element 2 was manufactured in the same manner as thelight-emitting element 1 except for usingtris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(tBuppm)₃]) represented by Structural Formula (vii) instead of[Ir(dmdppr-P)₂(dibm)], the thickness of ITSO serving as the firstelectrode 101 was set to 70 nm and the thickness of the layer 114 ncontaining the condensed aromatic compound or the condensedheteroaromatic compound in the electron-transport layer 114 was set to15 nm.

(Method for Manufacturing Comparative Light-Emitting Element 2)

The comparative light-emitting element 2 was manufactured in the samemanner as the light-emitting element 1 except for using BPhen instead ofNBPhen in the light-emitting element 2.

(Method for Manufacturing Light-Emitting Element 3)

The light-emitting element 3 was manufactured basically in the samemanner as that of the light-emitting element 1; however, the thicknessof the first electrode 101 was set to 70 nm and the hole-transport layerwas formed by deposition of3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn)represented by Structural Formula (viii) to a thickness of 20 nm. Thelight-emitting layer was formed by deposition of7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by Structural Formula (ix) andN,N′-bis(dibenzofuran-4-yl)-N,N-diphenylpyrene-1,6-diamine(abbreviation: 1,6FrAPrn-II) represented by Structural Formula (x) witha weight ratio of 1:0.05 (cgDBCzPA:1,6FrAPrn-II) to a thickness of 25nm. As the electron-transport layer 114, the layer 114 n containing thecondensed aromatic compound or the condensed heteroaromatic compound wasformed using cgDBCzPA to a thickness of 5 nm, and the layer 114 mcontaining NBPhen was formed to a thickness of 10 nm.

(Method for Manufacturing Comparative Light-Emitting Element 3)

The comparative light-emitting element 3 was manufactured in the samemanner as the light-emitting element 1 except for using BPhen instead ofNBPhen in the light-emitting element 3.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method. Note that the light-emitting element 1and the comparative light-emitting element 1 emit red phosphorescentlight; the light-emitting element 2 and the comparative light-emittingelement 2 emit green phosphorescent light; and the light-emittingelement 3 and the comparative light-emitting element 3 emit bluefluorescent light. The layer 114 n containing the condensed aromaticcompound or the condensed heteroaromatic compound contains the condensedheteroaromatic compound in the light-emitting elements 1 and 2 and thecomparative light-emitting elements 1 and 2, and contains the condensedaromatic compound in the light-emitting element 3 and the comparativelight-emitting element 3.

The light-emitting elements 1 to 3 and the comparative light-emittingelements 1 to 3 were each sealed using a glass substrate in a glove boxcontaining a nitrogen atmosphere so as not to be exposed to the air(specifically, a sealing material was applied onto an outer edge of theelement and UV treatment and heat treatment at 80° C. for 1 hour wereperformed at the time of sealing). Then, reliability of theselight-emitting elements was measured. Note that the measurements werecarried out at room temperature (25° C.).

FIG. 13 shows current density-luminance characteristics of thelight-emitting element 1 and the comparative light-emitting element 1;FIG. 14 shows luminance-current efficiency characteristics thereof; FIG.15 shows voltage-luminance characteristics thereof; and FIG. 16 showsemission spectra thereof. FIG. 17 shows current density-luminancecharacteristics of the light-emitting element 2 and the comparativelight-emitting element 2; FIG. 18 shows luminance-current efficiencycharacteristics thereof; FIG. 19 shows voltage-luminance characteristicsthereof; and FIG. 20 shows emission spectra thereof. FIG. 21 showscurrent density-luminance characteristics of the light-emitting element3 and the comparative light-emitting element 3; FIG. 22 showsluminance-current efficiency characteristics thereof; FIG. 23 showsvoltage-luminance characteristics thereof; and FIG. 24 shows emissionspectra thereof.

The results show that both the light-emitting elements and thecomparative light-emitting elements exhibit very favorable initialcharacteristics.

Then, these light-emitting elements were subjected to heat resistancetests. First, current values were measured when these elements were madeto emit light at 1000 cd/cm². Using the current values, luminances anddrive voltages were further measured. Next, each element was kept in aconstant temperature bath at 85° C. and taken out after a predeterminedtime. After the element was sufficiently cooled down, the element wasmade to emit light at room temperature using the initially measuredcurrent value, and the luminance and the drive voltage were measured.Results are shown in FIGS. 25A and 25B and FIGS. 26A and 26B.

FIGS. 25A and 25B are graphs showing heat exposition time in theconstant temperature bath and luminance changes. FIG. 25A shows resultsof the comparative light-emitting elements 1 to 3, and FIG. 25B showsresults of the light-emitting elements 1 to 3. These graphs indicatethat as the length of time of heat exposition of the comparativelight-emitting elements 1 to 3 at 85° C. increases, the emissionintensities thereof decrease when the same current is made to flow. On,the other hand, the light-emitting elements 1 to 3 do not show aluminance decrease.

FIGS. 26A and 26B are graphs showing heat exposition time in theconstant temperature bath and voltage changes. FIG. 26A shows results ofthe comparative light-emitting elements 1 to 3, and FIG. 26B showsresults of the light-emitting elements 1 to 3. FIG. 26A indicates thatthe light-emitting element 3 and the comparative light-emitting element3 in which the layer 114 n containing the condensed aromatic compound orthe condensed heteroaromatic compound contains the condensed aromaticcompound show little change in voltage with respect to heat expositiontime at 85° C. On the other hand, FIG. 26B indicates that thecomparative light-emitting elements 1 and 2 in which the layer 114 ncontaining the condensed aromatic compound or the condensedheteroaromatic compound contains the condensed heteroaromatic compoundshow significant changes in voltage due to high-temperature exposition.However, it also indicates that the light-emitting elements 1 and 2 inwhich the layer containing NBPhen is provided in contact with the layer114 n containing the condensed aromatic compound or the condensedheteroaromatic compound show little change in voltage.

As described above, the light-emitting elements and the comparativelight-emitting elements have similarly favorable initialcharacteristics, but show a great difference as a result ofhigh-temperature exposition. An important point here is that theirinitial characteristics are favorable and show little change. Inaccordance with one embodiment of the present invention, alight-emitting element with improved reliability at high temperature aswell as with maintained performance as a light-emitting element can beobtained.

Example 2

In this example, light-emitting elements (light-emitting elements 4 to6) of one embodiment of the present invention will be described.Structural formulae of organic compounds used in the light-emittingelements 4 to 6 are shown below.

Methods for manufacturing the light-emitting elements 4 to 6 of thisexample will be described below.

(Method for Manufacturing Light-Emitting Elements 4 to 6)

First, a film of indium tin oxide containing silicon oxide (ITSO) wasformed over a glass substrate by a sputtering method, so that the firstelectrode 101 was formed. The thickness thereof was 110 nm and theelectrode area was 2 mm×2 mm. Here, the first electrode 101 functions asan anode of the light-emitting element.

Next, as pretreatment for forming the light-emitting element over thesubstrate, UV-ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for one hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate was cooled down for about 30 minutes.

Then, the substrate over which the first electrode 101 was formed wasfixed to a substrate holder provided in the vacuum evaporation apparatusso that the surface on which the first electrode 101 was formed faceddownward. The pressure in the vacuum evaporation apparatus was reducedto about 10⁻⁴ Pa. After that, over the first electrode 101,9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carabzole (abbreviation:PCzPA) represented by Structural Formula (xii) and molybdenum(VI) oxidewere deposited by co-evaporation by an evaporation method usingresistance heating, so that the hole-injection layer 111 was formed. Thethickness of the hole-injection layer 111 was set to 50 nm, and theweight ratio of PCzPA to molybdenum oxide was adjusted to 4:2(=PCzPA:molybdenum oxide).

Next, a film of PCzPA was formed to a thickness of 10 nm over thehole-injection layer 111 to form the hole-transport layer 112.

Further, over the hole-transport layer 112, the light-emitting layer 113was formed by co-evaporation of9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by Structural Formula (xiii) andN,N′-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPm) represented by Structural Formula(xiv) with a weight ratio of 1:0.04 (=CzPA:1,6mMemFLPAPrn) to athickness of 25 nm.

Then, the electron-transport layer 114 was formed over thelight-emitting layer 113 in such a manner that a 10 nm thick film ofCzPA was formed (the layer 114 n containing the condensed aromaticcompound or the condensed heteroaromatic compound) and a 15 nm thickfilm of 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline(abbreviation: NBPhen) represented by Structural Formula (vi) was formed(the layer containing NBPhen).

After the formation of the electron-transport layer 114, lithiumfluoride (LiF) was deposited by evaporation to a thickness of 1 nm, sothat the electron-injection layer 115 was formed. Lastly, aluminum wasdeposited by evaporation to a thickness of 200 nm to form the secondelectrode 102 functioning as a cathode. Thus, the light-emittingelements 4 to 6 in this example were manufactured.

The light-emitting elements 4 to 6 were each sealed using a glasssubstrate in a glove box containing a nitrogen atmosphere so as not tobe exposed to the air (specifically, a sealing material was applied ontoan outer edge of the element and UV treatment and heat treatment at 80°C. for 1 hour were performed at the time of sealing). Then, reliabilityof these light-emitting elements was measured. Note that themeasurements were carried out at room temperature (25° C.).

FIG. 27 shows current density-luminance characteristics of thelight-emitting elements 4 to 6; FIG. 28 shows luminance-currentefficiency characteristics thereof; FIG. 29 shows voltage-luminancecharacteristics thereof; and FIG. 30 shows emission spectra thereof.

The results show that the light-emitting elements exhibit very favorableinitial characteristics.

FIG. 31 shows measurement results of luminance changes with respect todriving time under constant current density conditions at an initialluminance of 5000 cd/m². It is found from FIG. 31 that, although eachelement shows favorable characteristics, the light-emitting element 5shows more favorable characteristics than the light-emitting element 6and the light-emitting element 4 shows more favorable characteristicsthan the light-emitting element 5.

Here, as NBPhen used in the layer containing NBPhen, materials withdifferent impurity concentrations (samples 1 to 3) are used in thelight-emitting elements 4 to 6, and the samples 1 to 3 were used in thelight-emitting elements 4 to 6, respectively.

Impurities in NBPhen were detected using the following detectors:ACQUITY UPLC by Waters Corporation, Xevo G2 Tof MS by WatersCorporation, and ACQUITY UPLC PDA eλ by Waters Corporation.

In analysis, a solution obtained by dissolution of 1 mg of each samplein 2 mL of chloroform and then dilution with acetonitrile 10-fold wasused as a measurement sample. The analysis was carried out at 40° C.using ACQUITY UPLC BEH C8 Column by Waters Corporation (particlediameter: 1.7 μm, 100 mm×2.1 mm) as a column, under the conditions whereMobile Phase A was acetonitrile and Mobile Phase B was a 0.1% formicacid aqueous solution, in a gradient manner in which the proportion ofMobile Phase A was increased at a flow rate of 0.5 mL/min to reach 65%,held for 1 minute, and then increased at a constant rate to reach 95% 10minutes later. The injection amount was 5 μL.

FIGS. 32 to 34 show chromatograms obtained by measurement (detector:photodiode array (PDA) (absorption wavelength: 210 nm to 500 nm)). Notethat FIG. 32 shows a measurement result of NBPhen used in thelight-emitting element 4 (the sample 1); FIG. 33 shows a measurementresult of NBPhen used in the light-emitting element 5 (the sample 2);and FIG. 34 shows a measurement result of NBPhen used in thelight-emitting element 6 (the sample 3). Note that in each of FIGS. 32to 34, the horizontal axis represents time (min) and the vertical axisrepresents intensity (arbitrary unit). The content percentage of animpurity in each sample was obtained by calculating a peak area from thechromatogram. In the calculation of the peak area, a peak detectedwithin one minute was excluded because the peak resulted from chloroformused for dissolving the material. In addition, a mass spectrum wascalculated for each peak.

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method. Capillary voltage and sample cone voltage wereset to 3.0 kV and 30 V, respectively. Detection was performed in apositive mode.

Among substances detected with the PDA, m/z=585 is attributable toNBPhen. It can be inferred from the mass spectrum in FIG. 35 that animpurity 1 (m/z=619) is a chlorine mono-substituted compound of NBPhenwhich is represented by the following structure formula, though thesubstitution site is unspecified.

The analysis results show that the proportion of the peak at m/z=619which can be considered to be an impurity is 0.00% in the sample 1,0.22% in the sample 2, and 0.29% in the sample 3.

Furthermore, the amount of chlorine was measured by combustion ionchromatography. The analysis was carried out using an automatic samplecombustion apparatus AQF-2100H by Mitsubishi Chemical Analytech Co.,Ltd. and an ion chromatography system Dionex ICS-2100 by Thermo FisherScientific Inc.

Approximately 13 mg of each sample was weighed and put in a ceramic boatas a combustion sample. The heater temperature in the combustionapparatus was 1000° C. on the entrance side and 900° C. on the exitside. Gases of Ar, O₂, and humidified Ar were kept flowing at flow ratesof 200 mL/min, 400 mL/min, and 100 mL/min, respectively. An absorptionsolution (pure water to which 30 ppm of a phosphoric acid was added asan internal reference in the ion chromatography) was subjected tobubbling with those gases so as to absorb gases generated at the time ofcombustion.

Sample combustion was carried out in such a manner that a boatcontroller was used and the boat was moved under certain conditions sothat the sample was reacted with oxygen at high temperature. Theconditions for boat movement are as follows. Assuming that the samplesetting position was 0 mm, the boat was moved to a position of 130 mm at20 min/sec and stopped for 90 sec. Then, the boat was moved to aposition of 160 mm at 0.12 min/sec and stopped for 90 sec. Lastly, theboat was moved to the end of a combustion tube, i.e., a position of 265mm at 20 mm/sec, stopped for 90 sec, and then collected. The amount ofchlorine was measured by introducing 100 μL of the absorption solutionwhich had absorbed gases generated by the above combustion into the ionchromatograph.

Ion chromatography analysis was carried out at 35° C. using columns ofDionex IonPac AG20 (4 mm×50 mm) and Dionex IonPac AS20 (4 mm×250 mm).KOH was used as an eluent and its flow rate was set to 1.0 mL/min.Gradient measurement was carried out in which the concentration of KOHwas increased from 10 mmol/L to reach 15 mmol/L after 7 min and 40mmol/L after 18 min.

A conductivity detector was used as the detector. A calibration curvewas created using an anion mixed reference solution purchased from KantoChemical Co., Inc.

Analysis results show that the amount of chlorine in the sample 1 is13.5 ppm, the amount of chlorine in the sample 2 is 114.5 ppm, and theamount of chlorine in the sample 3 is 159.2 ppm. These results and UPLCresults of impurity content percentages are listed in Table 1.

TABLE 1 NBPhen F Cl Br S UPLC Lot No. ppm (mg/L) ppm ppm ppm Proportionof +Cl Sample 1 0.4 13.5 ND 3.2 0.00% Sample 2 0.5 114.5 ND 1.7 0.22%Sample 3 0.4 159.2 0.8 1.4 0.29% ND: Not Detected

The data of the light-emitting elements 4 to 6 described above also showthat a light-emitting element containing a smaller amount of NBPhenderivatives mono-substituted by chlorine has higher reliability. Theseresults suggest that, with the use of a material in which the amount ofchlorine in NBPhen is 100 ppm or less for a light-emitting element,deterioration of the light-emitting element can be minimized, so that ahighly reliable light-emitting element can be obtained. Meanwhile, thisimpurity concentration is equivalent to 1.0×10⁻² g/kg as the chlorineconcentration in NBPhen solid, and 1.7×10⁻¹ g/kg as the concentration ofthe chlorine mono-substituted compound in NBPhen solid.

This application is based on Japanese Patent Application serial no.2013-166870 filed with Japan Patent Office on Aug. 9, 2013 and JapanesePatent Application serial no. 2013-269839 filed with Japan Patent Officeon Dec. 26, 2013, the entire contents of which are hereby incorporatedby reference.

What is claimed is:
 1. A light-emitting element comprising: a firstelectrode; a first layer over the first electrode, the first layercomprising one of a condensed aromatic compound and a condensedheteroaromatic compound; a second layer over and in contact with thefirst layer, the second layer comprising NBPhen represented by thefollowing formula (vi)

and a second electrode over the second layer, wherein the condensedheteroaromatic compound is different from NBPhen, wherein the NBPhencomprises a chlorine mono-substituted compound of NBPhen as an impurity,and wherein a concentration of the chlorine mono-substituted compound ofNBPhen is at 1.7×10⁻¹ g/kg or less.
 2. The light-emitting elementaccording to claim 1, wherein the condensed heteroaromatic compoundcomprises a condensed ring skeleton, and wherein the condensed ringskeleton includes two nitrogen atoms.
 3. The light-emitting elementaccording to claim 1, wherein the light-emitting element is capable ofemitting phosphorescent light.
 4. The light-emitting element accordingto claim 1, wherein the first layer further comprises an iridiumcomplex.
 5. The light-emitting element according to claim 4, wherein apart of the first layer comprises the iridium complex.
 6. Alight-emitting device comprising: the light-emitting element accordingto claim 1; and a unit for controlling the light-emitting element.
 7. Alighting device comprising: the light-emitting element according toclaim 1; and a unit for controlling the light-emitting element.
 8. Anelectronic device comprising the light-emitting device according toclaim
 6. 9. A light-emitting element comprising: a first electrode; afirst layer over the first electrode; a second layer over and in contactwith the first layer, the second layer comprising NBPhen represented bythe following formula (vi)

and a second electrode over the second layer, wherein the second layerfurther comprises a chlorine mono-substituted compound of NBPhen as animpurity, and wherein the second layer comprises chlorine at 1.0×10⁻²g/kg or less.
 10. The light-emitting element according to claim 9,wherein the first layer comprises a heteroaromatic compound which isdifferent from NBPhen.
 11. The light-emitting element according to claim10, wherein the heteroaromatic compound comprises a condensed ringskeleton including three or more rings.
 12. The light-emitting elementaccording to claim 10, wherein the heteroaromatic compound includes twonitrogen atoms.
 13. The light-emitting element according to claim 10,the first layer further comprising an iridium complex.
 14. Thelight-emitting element according to claim 13, wherein a part of thefirst layer comprises the iridium complex.
 15. The light-emittingelement according to claim 13, wherein the iridium complex is capable ofemitting phosphorescent light.
 16. A light-emitting device comprisingthe light-emitting element according to claim
 9. 17. A lighting devicecomprising the light-emitting element according to claim
 16. 18. Anelectronic device comprising the light-emitting element according toclaim 16.